
A unit of statistical significance, where higher sigma indicates stronger evidence.Sigma (σ) is a statistical measure of significance, indicating how many standard deviations an observed result is from the expected background. A higher sigma means stronger evidence against the null hypothesis. In physics, a 5-sigma result is the gold standard for a discovery, such as the Higgs boson in 2012.
The use of sigma in physics was popularized in the 20th century, particularly in particle physics, where the convention of 5-sigma for discovery was established by the 1980s.
When measuring a signal, scientists compare it to the expected background noise. The sigma value is calculated as the difference between the observed and expected values divided by the standard deviation of the background. A 3-sigma result indicates a 0.3% chance of being a statistical fluke, while 5-sigma reduces that to 0.00006%.
Sigma is used in particle physics (e.g., CERN experiments), cosmology (e.g., cosmic microwave background), and medical trials to assess the reliability of results.
The 2012 discovery of the Higgs boson was announced with a significance of 5.9 sigma, meaning the chance of it being a background fluctuation was less than one in a billion.









